


Undertale smut

by briana



Category: Undertale (Video Game)
Genre: Cutting, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), F/M, Female Frisk, Gaster Sans, Hand Job, NSFW, Sans - Freeform, Smut, Underground, surface - Freeform
Language: English
Status: In-Progress
Published: 2016-09-05
Updated: 2016-09-06
Packaged: 2018-08-13 03:28:56
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 2,772
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7960687
Author URL: https://archiveofourown.org/users/briana/pseuds/briana
Summary: <blockquote class="userstuff">
              <p>A collection of undertale smut</p>
            </blockquote>





	1. Gaster Sans x Emo Frisk (part one)

**Author's Note:**

> (Gaster Sans is the eldest brother of Sans and Papyrus in this)

Frisk sat on the couch of the skeleton brothers house. It's been about a month since she let the monsters free from the underground. She moved in with Toriel when they got back to the surface. Though she never told any of the monsters about her parents or family in general. As of right now Toriel was out getting ingredients for pie. Pap was out with Undyne getting ingredients for spaghetti. The monsters and Frisk were basically having a family dinner tonight. This left Frisk with the Sans brothers. 

"Sans! I swear to Asgore if you make one more pun or joke I WILL punch you!" yelled Gaster Sans. "Why" said Sans "are they not humerus or puny". Frisk gave a small laugh, know watching the two skeletons. "See, the kiddo thinks they are" said Sans, now grinning. At this point Gaster Sans hand his hand in a fist in the air about to strike down on him. Sans ran to his room quicker than his brothers fist, locking the door.

Gaster Sans growled and sat next to Frisk. "Do you not have a girl coming over before we have dinner?" she asked. "No" he answered. He looked at Frisk with a flirty look. "Not when I have you over~". Frisk rolled her eyes with light pink dusting her cheeks. She knew how he was, a fuck boy. She had seen 3 or 4 of the girls he has slept with. Only one was human though. Frisk had developed a crush for him, but she was sure that he didn't feel the same way. 'Like I'll ever have a chance with him' she thought as she brought her legs up to her chest. "Are you ok Frisk?" Gaster Sans asked worried. "Yea.. I'm fine... I'm just going to go to the bathroom for a second". "Ok.. if you need anything just ask". 'He doesn't need to know about it'. She repeated this over in her head until she got to the bathroom. She open the cabinet that was for her. She unfolded a towel to reveal a razor blade.

Sans soon came out of his room. "I'm going to go somewhere". Gaster Sans watched as his brother stopped just before he closed the door. "Where's Frisk" he asked. "In the bathroom.. doing something" he said the last part in a whisper. "Ok, just make sure she's fine". "Just go already, I'm not going to let anything happen to her". With that Sans left to wherever he was going.

Gaster Sans was beginning to suspect Frisk was doing more than going to the bathroom. He waited a little bit longer before going to check on her. He walked to the bathroom door and was about to knock when he noticed she forgot to close the door. He pushed the door open gently to not startle Frisk. His eyes grew when he saw what she was doing.

Only after the third cut that she noticed Gaster Sans standing in front of her with a shocked expression. Frisk dropped the bloody razor blade, surprised to see him standing before her. 'Did I forget to close the door' she thought. Her mind was racing a mile a second."I-I-I.. I..". Frisk didn't know what to say. "W-why didn't you say anything?!". Gaster Sans was so confused and shocked. Frisk stayed silent. "At least tell me why your doing this...". Frisk pondered on whether or not she should say what she's been keeping from everyone. "Frisk please.. you can tell me". Gaster Sans pulled her next to him on the floor, but still held her with his head on hers. At this point Frisk was crying into his leather jacket. "I-I-I've never t-told you about m-m-my par-parents, w-w-well there's a g-good reason to that" Gaster Sans started to gently rub her back. "M-m-my fa-father wasn't a v-very nice man to me". Gaster Sans growled and squeezed her know what she meant. "A-and my mom was a drunk.. s-so she wasn't much help... the main reason I fell down into the underground was because I was running from him... that's why I never said anything about my family". Gaster Sans was silent at first, but then said something that Frisk never expected.

"Frisk your beautiful no matter what others my say... your prettier than any girl I've met, monster and human. I would choose you over any girl any given day".

 

 

To be continued


	2. Gaster Sans x Emo Frisk (smut)

**Summary for the Chapter:**

> (This is the smut part of the last chapter. This is my first one so don't judge to harshly. I hope you enjoy it)

**Notes for the Chapter:**

> There will be a smut warning when the smut starts.

"Frisk your beautiful no matter what others my say... your prettier than any girl I've met, monster and human. I would choose you over any girl any given day".

Frisk couldn't believe this was coming from Gaster Sans, it was to good to be true. "Sans.. are you drunk or has your heat cycle started...". Sans sighed at this. "No this not a dream, I'm not drunk, and my heat cycle hasn't started". Sans then picked Frisk up bridal style. Frisk, surprised by this, wrapped her arms around his neck to avoid falling. He chuckled at this. He went into his room, put Frisk on his bed, and locked the door. "Sans.. what are you doing...?"

-Smut Warning-

Sans crawl on top of Frisk and leaned down to her ear. "If your not going to believe me when I say that I think that your beautiful and that I love you differently then perhaps I can show you in a different way~". His voice was husky and full of lust, making Frisk shutter. He waited to see if she would abject, but she didn't. With this he continued by taking off her black hoodie, tank top, and jeans leaving her in her bra and underwear. Frisk blushed and turned away. Sans took the opportunity to start kissing her neck. Frisk gasped in surprise, but soon pushed him far enough to where he was look at her face to face. His eye was glowing brightly in the darkness of his room. "Do..do you want me to stop? I can stop if you want me to". Frisk then started tugging at his leather jacket. Sans grinned at this. "It's only fair if you do it yourself sweetheart~". Frisk hesitated, but started to take his cloths off. She managed to take his jacket off, but was fumbling with his belt. She finally managed to get his belt off, but stopped there. All she could was blush as she stared at the lump in his pants. "Save that for later, I want to do something for you~".

At first Frisk was confuse, but before she could ask what he meant he put her a sitting position and took her underwear off. He straddled her torso and takes her bra off. Frisk covered her breasts, but Sans moved her arms. "I already told you Frisk.. your beautiful". Sans put his hand on her shoulder, and then starts to trace them down her side. Frisk shutters at this. He left his hand on her thigh for a few seconds and then pulls his hand away. Frisk whines in frustration at this. "Move over so I can lay down". She was confused as to why, but listened. He lays down, sitting up slightly, and pulls Frisk in front of him with her back resting on him. Frisk tensed up at this considering the position and how she was naked. Sans starts to stroke her inner thigh. At this point she knew what he was planing on doing. Sans started rubbing her down, teasing her clit here and there. Frisk shuttered, moaning every now and then. "My my my, I didn't know you could get this excited just from just me touching you~".

Frisk could feel herself nearing her climax, but Sans decided to be a tease and stopped before she could. "I'm not letting you off that easily, but I think I should get something in return for this~". With that Sans put Frisk next to him, sat up and pulled his pants down. Frisk could only blush and stare at the yellow erection. "I won't force you to give me oral, but I at least want a hand job... if you know what that is" Sans said the last part smirking. Frisk knew what it was, but she was worried that she wouldn't impress him. As if reading her mind Sans spoke "don't worry, you'll be fine". With that Frisk grabbed his erection and started rubbing him down. Sans grunted and groan in pleasure as she continued. She experimented with different speeds and ways of touching, seeing what he reacted to most. She stopped when it started to twitch.

Sans was a panting mess. "F-for your *pant* first time that w-was *pant* fucking amazing". Frisk felt proud of herself. It's been a bit since she felt like this, she was happy with herself. "Are you ready to do the real deal? Don't worry, I'll do the work". The thing was Frisk was worried, this was her first time after all. Sans gently pushed her to the bed, positioning himself at her entrance. Both of his arms where on either side of her head. "It's going to hurt so to make it quicker I'm going to go into you fully, first thrust ok". Frisk nodded, but she was in great pain as Sans thrusted into her. Frisk couldn't help the tears that fell. Sans just kept kissing her here and there to help her with the pain. Sans waited patiently for the sign to go, but that didn't stop his body from shaking from the pleasure he was getting. Frisk soon nodded for him to go. At first he start slow and sweet, but as he noticed Frisk was used to his size he became rough and dominant. The room full of groans, moans, grunts, and whines of pleasure. Frisk felt a knot forming in the pit of her stomach. The knot grew tighter. Frisk felt like the knot was going to burst. Sans took note of this and thrusted fast and deeper than before. He was soon going inhuman speed in his thrusts. Frisk reached her climax, moaning out in ecstasy. Sans soon followed and climaxed as well.

He pulled out of Frisk and collapsed next to her panting. "W-w-we might as well *pant* t-take a nap w-while we wait *pant* for the others". Frisk could only nod in response. Sans pulled the covers over them and rapped his arms around Frisk. She soon fell asleep in him arms. He kissed your forehead "goodnight my love". With that he fell asleep.

The end

**Notes for the Chapter:**

> Hope you enjoyed
> 
> If you wish to make a request then comment what character you want and if it's with the reader or with another character. If it's a reader one then I will need you to say what gender. I'm willing to do same gender smut too. If there's a specific detail (position, action, place, ect.) you want in the smut then go ahead and tell me that in the request.


	3. Sans x Frisk (part one)

**Summary for the Chapter:**

> First part of Sans x Frisk smut. Hope you enjoy.

Frisk walked through the snow to the skeleton brothers house as fluffy flakes of snow lightly fell on the ground. She was trying to get there before a predicted snow storm came in. She was glad she left the store when she heard about the storm. It began to snow heavily when she was close to the house. She ran the rest of the way to her destination. She shook herself to get any loose snow off of her before her knock on the door. She heard some muffled noises of someone walking.

The door opened to reveal Sans. "Damn kid how are you not a walking icesicle right now, it's freezing" remarked Sans as he moved over to let Frisk in. Frisk laughed as she entered. "You probably would be so cold if you turned the AC on and put some pants on instead of shorts you wouldn't be so cold" answered Frisk. "Well you know how much of a lazy bone I am, so I stick with a blanket and sleep". Frisk rolled her eyes at this and went to turn the AC on. "By the way where's Papyrus?" Frisk questioned. "He's going to be stuck at Undyne's house".

Frisk blushed a little when Sans said they were alone together. She immediately took a liking to the skeleton when they first met in the underground. The strong feelings had first developed about a month after she freed the monsters from the underground.

Humans didn't like that monsters were rouming around with them. They preferred to stay away from them, but the people who liked to cause trouble wouldn't. People dumb enough to go for Sans would do it because of his size, but they would soon regret it. He was up to Frisk's shoulder, but was two years older.

Frisk waited for the AC to turn on before sitting next to Sans on the couch. "So... what do you want to do Sans?" Frisk asked. "Take a nap with you". Frisk blushed at this, but agreed anyway. Frisk layed in front of Sans and closed her eyes. Sans pulled a blanket over him and Frisk. Frisk soon fell into a deep slumber. Frisk began to awake and open her eyes. What she saw was not what she expected to see.

To be continued

**Notes for the Chapter:**

> Hope enjoyed. Smut will be on the next chapter.
> 
> If you wish to make a request then comment what character you want and if it's with the reader or with another character. If it's a reader one then I will need you to say what gender. I'm willing to do same gender smut too. If there's a specific detail (position, action, place, ect.) you want in the smut then go ahead and tell me that in the request.


	4. Sans x Frisk (smut)

**Summary for the Chapter:**

> Smut part of the last chapter. Hope you enjoy.

Frisk began to awake and open her eyes. What she saw was not what she expected to see.

She fell asleep on the couch with Sans, but they were in his room with him laying on top of her. Frisk blushed at this. Sans head was laying on her chest. What was worse is that his crotch was on top of hers. His arms were rapped around her, so she had to wake him up to get him off. "Sans... Sans wake up...". Sans began to laugh with his eyes closed. Frisk blushed at the fact he probably planned this. "Could you get off of me please". "Why would I do that?" Sans asked while opening his eyes. "Because this is an akward position were in". "It may be akward for you, but for me...". Sans pressed his crotch on Frisk's, causing her to gasp and moan a bit. "This is perfect".

Sans moved up to where his head was in front of her neck. He took his hands and pinned her arms on either side. A blue tongue slithered out of his mouth and licked her neck. Frisk gasped from the contact. Sans licked more roughly as he searched for her most sensitive spot. When he found it Frisk moaned quietly, making Sans grin. He licked and nipped at the spot till he became bored.

He then began to take off her shirt. When he took it off he looked at Frisk in the eyes, seeing if he could continue. Frisk stared at him, her face felt as if it was on fire. Sans chuckled at this and took this as a sign to continue. He took off her bra, pants, and underwear. Frisk blushed as she watched him take his jacket and shirt off. Frisk whined when he didn't take off his shorts. Sans chuckled at this. "Be patient kiddo, I want to do something first". 

Sans began kissing Frisk deeply. She felt something lick her bottom lip, causing her to gasp in surprise. This "thing" took this as a chance to slither in her mouth and explore. Sans pulled away when they needed air. When she got her breathing under control Frisk looked up at Sans. She saw what invaded her mouth hanging out of his mouth. It was a blue tongue. Sans retracted it back into his mouth.

He moved to where he was in between her legs. She knew what he was going to do. She had sex with a past lover before, but only once. He started kissing her inner thigh. He then started to rubbing his tongue on her womanhood. Frisk started moaning and gripped at a pair of Sans ribs. Sans groaned at this. Frisk noticed this and started rubbing them. Sans continued by thrusting his tongue into her. Frisk moaned loudly at this. His tongue felt a bit like gel and was slightly cold. After a bit he retracted his tongue.

Frisk whined at this. Sans sat up and took off his shorts revealing his blue erection. He got into position, but stopped to look up to meet Frisk's eyes. "Are you sure you want me to continue". Frisk could only nod in response. He thrusted in and waited for her to get used to him. Frisk soon moaned. Sans took this as a sign and started to thrust. The room was full of moans and groans. Frisk clawed at the couch when she hit her climax. Sans picked up the pace and soon followed. He layed on top of Frisk panting along with her. He grabbed the blanket from the ground. He moved beside Frisk, who already fell asleep. He pulled the blanket over them and kissed her forehead. "Goodnight kiddo" he said before letting sleep take over him.

The end

**Notes for the Chapter:**

> Hope you enjoyed.
> 
> If you wish to make a request then comment what character you want and if it's with the reader or with another character. If it's a reader one then I will need you to say what gender. I'm willing to do same gender smut too. If there's a specific detail (position, action, place, ect.) you want in the smut then go ahead and tell me that in the request.

**Author's Note:**

> Hope you enjoyed
> 
>  
> 
> If you wish to make a request then comment what character you want and if it's with the reader or with another character. If it's a reader one then I will need you to say what gender. I'm willing to do same gender smut too. If there's a specific detail (position, action, place, ect.) you want in the smut then go ahead and tell me that in the request.


End file.
